1. Field of the Invention
The present invention relates in general to the semipermanent poling of materials that exhibit pyroelectric and/or piezoelectric properties, and more specifically relates to the continuous poling of such materials.
2. Description of the Prior Art
Only recently has it been known that certain polymer materials that may be extruded in a continuous film possess pyroelectric and/or piezoelectric properties. Prior to this discovery, crystalline materials were known to exhibit such properties, but forming a continuous layer of material possessing both properties was not possible due to the physical nature of crystalline material. Accordingly, prior art poling techniques are directed to the poling of relatively small segments of material.
A standard technique for poling only a segment of material is to electrically contact both sides of the segment with conductive layers that serve as poling electrodes to which a poling potential is applied for establishing an electric field across the segment. However, this technique has proven unsatisfactory for continuous lengths of material because if the electric field exceeds the breakdown strength of the material, as often happens at a defect or thinner than normal area, a short will occur between the two conductive layers. Such shorting may rupture the material and require shut-down of the poling operation.
Another known poling technique is disclosed in U.S. Pat. No. 3,761,746, wherein a segment of ferroelectric material is positioned inside a sealed chamber and has its planar surfaces exposed to ionized regions that provide a sufficient electric field to produce poling of the segment. Although this procedure apparently performs satisfactorily in poling a single segment of material, the requirement of a sealed chamber in which poling is performed would involve undue complexity for use in poling of a continuous sheet of material.